Communication through the use of wireless communication systems has achieved wide popularity in recent years. Multi-user, wireless communication systems of improved capabilities have been implemented as a result of advancements in communication technologies. Communication pursuant to such multi-user, wireless communication systems can be affordably made, further increasing the popularity of usage of such systems.
In a wireless communication system, a communication channel formed between a sending station and a receiving station is a radio channel defined upon a portion of the electromagnetic spectrum. Because a radio channel forms a communication link, a wireline connection is not required to be formed between the sending and receiving stations to permit the communication of information between the stations. Communication by way of a wireless communication system is thereby permitted at, and between, locations at which the formation of a wireline connection would not be possible. Also, because a communication channel is formed of a radio channel, a radio communication system can be more economically installed as the infrastructure costs associated with a wireline communication system are significantly reduced.
A cellular communication system is exemplary of a wireless, multi-user radio communication system which has been made possible due to advancements in communication technologies and which has achieved wide levels of usage. A cellular communication system efficiently utilizes the portion of the electromagnetic spectrum allocated thereto. A plurality of fixed-site base stations are installed throughout a geographical area. By transmitting relatively low-power signals, the same frequencies can be reused at different locations throughout the geographical area. Thereby, communications can be effectuated between more than one set of sending and receiving stations concurrently at separated locations throughout the area encompassed by the cellular communication system. Controlling the power levels at which signals generated during operation of a cellular communication system is important to minimize co-channel interference of concurrently-generated communication signals.
Various standards have been promulgated relating to various types of cellular communication systems, and various types of cellular communication systems have been constructed corresponding to such standards. The IS-95 and IS-98 interim standards, promulgated by the EIA/TIA, are exemplary of standards which pertain to a cellular communication system utilizing CDMA (code division multiple access) communication techniques. In a CDMA communication system, a plurality of concurrently-generated communication signals are generated concurrently upon a common channel. When such a communication scheme is utilized, the power levels of such communication signals must be regulated better to achieve optimal capacity.
Various standards are also being proposed for a so-called third-generation (3G), cellular communication system. Proposed standards predicated upon CDMA also set forth a scheme by which to regulate power levels of communication signals generated in such a system, referred to as a IS-95 3G system.
The interim standards and proposed IS-95 3G standard set forth, inter alia, requirements for closed-loop, power control in a cellular communication system constructed pursuant to such standard. And, more generally, because of the need to control power levels of signals generated during operation of a CDMA communication system, closed-loop power control schemes are advantageously implemented in such, as well as other, systems. In an exemplary closed-loop, power control scheme, power control bits are generated and transmitted by network infrastructure on a forward link channel to a mobile station. The power control bit is used, once received at the mobile station, to control the power levels at which reverse link communication signals are generated by the mobile station. Two-way power control can be effectuated in which power control bits are generated at the mobile stations, transmitted to the base station and used to control the power levels of signals generated on a forward link.
The radio communication channels upon which communication signals, including control information, such as the power control bits, must be communicated between the network infrastructure and a mobile station exhibit multi-path characteristics. That is to say, a signal actually received at, e.g., a mobile station, is actually a summation of the same signal transmitted by way of various different transmission paths to the mobile station. The same signal is received at the radio telephone, albeit at various time delays, as a result of such multi-path transmission. Analogously, multi-path characteristics also are exhibited upon an uplink channel upon which signals are transmitted by the mobile station.
Multi-path conditions on the communication channel might cause communication quality degradation, resulting in signal fading. Other communication system conditions might also result in signal fading. And, fading of the communication signal as the signal is transmitted upon the communication channel might prevent its accurate detection at its destination.
To counteract signal fading, closed-loop power control is utilized to cause power levels of signals communicated upon the communication channel to be increased. In the aforementioned CDMA system, e.g., power control bits transmitted to the mobile station are used by the mobile station to select the power levels of signals generated by the mobile station on the reverse link channel. In a two-way, power control scheme, power control bits transmitted to the mobile station are used at the base station to control the power levels of signals transmitted therefrom.
By increasing the power levels of the signals communicated on such channel, signal degradation, due to fading is, ideally, overcome. However, in the event of severe fading conditions, any reasonable power level increase in the power levels of the signals communicated on the communication channel would not result in appreciable communication quality increase. In other words, channel conditions might be so poor that increasing the power levels of the transmitted signals would not result in communication quality improvement.
Increasing the power level of the communication signal might also adversely affect communication qualities of other communication signals transmitted at the same time upon other channels. In the aforementioned, CDMA system, for instance, channels are defined by unique codes, and a plurality of signals are generated at the same time upon a common bandwidth. A signal, when received at a destination, must be decoded. Other signals transmitted upon the common bandwidth are considered to be noise. And, the power levels of such other signals, considered to be noise, must not be so high as to interfere with proper detection and decoding of the desired signal. Signals generated in a CDMA communication system of high power levels are therefore particularly likely to adversely affect communication qualities of other signals generated at the same time.
As noted above, increase in the power level of a communication signal in an attempt to overcome fading is ineffective to improve communication quality levels in deep fading conditions. And, because such an increase in power levels might adversely affect the communication qualities of other communications, care must be exercised when increasing the power levels of the communication signal.
A manner by which to effectuate power control which takes into account a determination whether a power level increase would benefit communication quality would therefore be advantageous.
It is in light of this background information related to communications by way of a non-ideal communication channel that the significant improvements of the present invention have evolved.